Cutaneous electrode

ABSTRACT

A windowed electrode assembly includes a foam layer having windows. Each window receives a corresponding gel pad that is sized such that it is contained by the window&#39;s sidewalls. The windowed electrode assembly includes a foam backing layer that forms a back wall for the windows such that each gel pad is encased by the window&#39;s sidewalls and back wall.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Patent ApplicationNo. PCT/US2013/062749 filed Sep. 30, 2013 and entitled “CUTANEOUSELECTRODE” which is hereby incorporated by reference in its entirety.

International Patent Application No. PCT/US2013/062749 claims thebenefit of U.S. Provisional Patent Application No. 61/707,859 filed Sep.28, 2012, which is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates generally to electrodes for medicaltherapy, and more specifically to a cutaneous electrode adapted forcutaneous stimulation of the ophthalmic nerves.

BACKGROUND

Neurological disorders such as seizure disorders are usually treatedwith medication. However, there are patients who are not helped bymedication—they may not be able to tolerate the side effects or themedication itself is not efficacious for their particular disorder. Thisis a significant problem in that seizure disorders can be lifethreatening. Moreover, the quality of life for victims of severeepilepsy can be severely impacted. Neuropsychiatric disorders such asdepression and ADHD are also typically treated with medications thathave deleterious side effects and lack of efficacy. To offer patientsrelief that medication alone cannot deliver, various neurostimulationmethods have been developed. For example, vagus nerve stimulation (VGS)has been shown to be therapeutically useful. Similarly, deep brainstimulation (DBS) and responsive neurostimulation (RNS) approaches areknown to have efficacy. But these neurostimulation techniques areinvasive as they require surgical implantation of electrodes. Thus,these techniques are relatively expensive and involve the dangersassociated with the surgical implantation of the electrodes.

To provide neurostimulation without the invasive dangers of prior arttechniques, an alternative neurostimulation therapy has been developedthat involves trigeminal nerve stimulation (TNS). For example, acutaneous embodiment of TNS involves the transcutaneous stimulation ofthe supraorbital nerves and/or the supratrochlear nerves in theforehead. Like other cranial nerves, the supraorbital and supratrochlearnerves arise through foramina in the skull. The supraorbital nervearises from the supraorbital foramen above the orbit. Since one has twoeyes, there are thus two supraorbital nerves that ascend verticallytoward the scalp from their respective foramen. The supratrochlear nerveis medial with regard to the supraorbital. But it also then ascendsvertically towards the hairline. There are thus two supratrochlearnerves, each arising from its respective orbit. A supraorbital nerve andsupratrochlear nerve thus associates with each orbit. The forehead isthus an ideal location to stimulate the trigeminal nerve in that thesupraorbital nerve and supratrochlear nerve associated with each orbitare located medially on the forehead. The skin and fascia over theforehead is relatively thin such that the supratrochlear andsupraorbital nerves are readily stimulated transcutaneously.

One approach to stimulate the supratrochlear and supraorbital nervesrequires a clinician to palpate for the supraorbital notch or foramen sothat a suitable electrode can be applied adjacent the notch. Theelectrode would be sized so that it would cover not only the trunk ofthe supraorbital as it arises from its foramen but also the trunk of thecorresponding supratrochlear nerve. To provide bilateral stimulation,the clinician would also palpate for the remaining supraorbital notchand apply another electrode accordingly. Although such an approachprovides advantageous neurostimulation for treatment of disorderswithout invasive implantations or deleterious pharmaceutical sideeffects, the treatment is burdened by the need for expert application ofthe electrodes. For example, if a lay person applies the electrodes inthis fashion and locates the electrodes too laterally on the forehead,the resulting bilateral current excited between the two electrodes maypenetrate to the brain. Thus, the application of electrodes in thisfashion required medical expertise, which greatly increases costs as thepatient must visit a medical facility daily for chronic treatments.

To provide efficacious trigeminal neurostimulation therapy without theneed for daily medical facility visits, a cutaneous electrode assembly10 as seen in TNS system 100 of FIG. 1 supports electrodes (notillustrated) such that if a patient medially centers electrode assembly10 across their forehead, the contained electrodes are then positionedover the supraorbital and/or supratrochlear trunks. To ensure themaximum coverage or stimulation of each supraorbital and supratrochlearnerve trunk, the patent may be instructed to align an inferior edge ofelectrode assembly just above their orbital arches. If electrodeassembly 10 has electrodes configured for bilateral stimulation of thetrigeminal, one or more electrodes will thus be on located above eachorbit and over the supraorbital notches such that a pulse transmittedbetween the electrical contacts for each orbit will conducts across thesupraorbital and supratrochlear nerve fibers as they arise from theirrespective orbits. Moreover, these nerve branches are relatively shallowwith regard to the forehead skin surface and thus readily stimulated byelectrode assembly 10.

A patient can easily apply electrode assembly 10 in the correct positionby centering it across the forehead median. Although electrode assembly10 has conductive gel so as to adhere to the forehead, a retainer device24 may also be used to help secure electrode assembly 10. A pulsegenerator 15 drives electrode assembly 10 through a cable 20. It isimportant that a patient be able to correctly position a TNS electrodeso that the appropriate nerves are stimulated without the risks ofcurrent penetration to the brain. Because a patient can readily positionelectrode assembly 10 medially on their forehead using a landmark suchas their nasal midline, the patient needs no knowledge of anatomy inthat regard yet they are positioning the electrode in an advantageouslocation for TNS therapy. Studies have shown that TNS carried out inthis fashion are significantly more efficacious than the use ofconventional VNS. Yet TNS is far less invasive, has much fewer risks,and considerably lower cost than VNS.

Although TNS is thus an attractive alternative to VNS, problems remainwith regard to it use. For example, it is conventional in the cutaneouselectrode arts to use a conductive gel to adhere an electrode to theskin. The gel is quite sticky and serves as both an adhesive and anelectrical conductor. It is thus conventional to apply EEG and EKGelectrodes using conductive gel. Similarly, conductive gel is used toapply TENS (transcutaneous electrical nerve stimulation) electrodes. Butsuch applications are relatively temporary. In contrast, the electricalstimulation from TNS may need to be applied for hours at a time such aswhile sleeping or even 24 hours a day. The forehead is a problematicenvironment for such long-term adhesion as the forehead skin isgenerally quite oily. Moreover, the excessive oil tends to make theforehead more prone to contaminates such as dust or dirt. An electrodeapplied with conductive gel to the forehead will thus tend to come offduring such relatively-long periods of time. This is problematic as theelectrode can only provide therapy while it is attached to the patient.Moreover, the peeling off of the electrode can induce arcing from theelectrode to the patient. Accordingly, there is a need in the art forimproved TNS electrodes.

SUMMARY

A windowed electrode assembly includes a foam layer having windows. Eachwindow receives a corresponding gel pad that is sized such that it iscontained by the window's sidewalls. The windowed electrode assemblyincludes a foam backing layer that forms a back wall for the windowssuch that each gel pad is encased by the window's sidewalls and backwall.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a subject wearing a cutaneous electrode for TNStherapy.

FIG. 2A is a perspective view of an example cutaneous electrodeassembly.

FIG. 2B is an exploded view of the electrode assembly of FIG. 2.

FIG. 3A is a plan view of an electrode assembly with alignment features.

FIG. 3B is a perspective view of the electrode assembly of FIG. 3A.

FIG. 3C is an exploded view of the electrode assembly of FIG. 3A.

FIG. 4 is a plan view of a unilateral windowed electrode assembly windowlayout.

Embodiments of the present invention and their advantages are bestunderstood by referring to the detailed description that follows. Itshould be appreciated that like reference numerals are used to identifylike elements illustrated in one or more of the figures.

DETAILED DESCRIPTION

Reference will now be made in detail to one or more embodiments of theinvention. While the invention will be described with respect to theseembodiments, it should be understood that the invention is not limitedto any particular embodiment. On the contrary, the invention includesalternatives, modifications, and equivalents as may come within thespirit and scope of the appended claims. Furthermore, in the followingdescription, numerous specific details are set forth to provide athorough understanding of the invention. The invention may be practicedwithout some or all of these specific details. In other instances,well-known structures and principles of operation have not beendescribed in detail to avoid obscuring the invention.

As used herein, an “electrode assembly” refers to a generally planarframework that supports one of more electrodes for cutaneous stimulationof the ophthalmic nerves on patient's forehead. As further used herein,an “ophthalmic nerve pair” refers to the supraorbital nerve andsupratrochlear nerve that arise from the same supraorbital arch ororbit. It is thus convenient for each electrode in an electrode assemblyto have a size sufficient to excite both nerves in a given ophthalmicnerve pair. As will be explained further below, the novel electrodeassemblies disclosed herein may be denoted as “windowed” electrodeassemblies in that a windowed electrode assembly encases each electrodein a window or cavity. In other words, a windowed electrode assembly hasa skin-facing planar surface that is configured to adhere to a patient'sforehead using medical-grade adhesive. The windows are defined withregard to this planar surface and backed by an opposing outward-facingsurface of the windowed electrode assembly. Each window encases acorresponding electrode that comprises conductive gel. This is quiteadvantageous in that adhesive surface of the windowed electrode assemblykeep the windowed electrode assembly removably fastened to a patient'sforehead without the possibility of the conductive gel oozing out fromthe applied windowed electrode assembly and leading to patientdiscomfort and reduction of therapeutic efficacy. Each conductive gelelectrode is then encased in that it is surrounded by the adhesiveskin-facing surface of the windowed electrode assembly, the sidewalls ofthe corresponding window, and a back wall of the corresponding window asdiscussed further herein.

Each windowed electrode assembly has a longitudinal extent sufficient toextend from the lateral portion of one supraorbital arch on a patient'sforehead to a lateral portion of the opposing supraorbital arch. Giventhis longitudinal extent, if a patient medially centers the electrodeassembly above their supraorbital arches with regard to their nasalmidline, the electrode assembly will extend substantially across eachsupraorbital arch. As will be explained further below, each lateral endof the longitudinally-extending windowed electrode assembly includes awindow positioned such that when the patient centers the windowedelectrode assembly as discussed above on their forehead, each ophthalmicnerve pair is covered by a corresponding window in the windowedelectrode assembly. Some example embodiments will now be discussed inmore detail. Referring now to FIG. 2A, a windowed electrode assembly 200is shown that addresses the problems discussed above with regard toconventional electrode design for TNS therapy. FIG. 2B is an explodedview of windowed electrode assembly 200. To adhere windowed electrodeassembly 200 to the forehead, the user first pulls off a flexibleplastic release liner 240. Prior to use, release liner 240 protects apair of gel pads 235, which are laterally positioned in an opposingfashion with regard to the longitudinal center of windowed electrodeassembly 200 in corresponding windows of a skin-facing foam layer 220.In this fashion, when windowed electrode assembly 200 is centered on theforehead analogously as shown in FIG. 1 (more generally, when thelongitudinal center of electrode assembly 200 is aligned with the nasalmidline/forehead midline), each electrode/gel pad 235 cover the trunksof the supraorbital and supratrochlear nerves in a correspondingophthalmic nerve pair as they ascend from the orbit superiorly towardsthe hairline. The excitation from windowed electrode assembly 200 isthus bilateral in that one gel pad 235 acts as a cathode (or anode) anda remaining gel pad 235 acts as the corresponding anode (or cathode). Ifthe excitation is AC, then the cathode and anode roles for gel pads 235are periodically reversed depending upon the current phase for the ACexcitation. As an electrical pulse is generated from one pad 235 to theother, the pulse will conduct across the supraorbital and supratrochlearnerve fibers to stimulate them. The resulting stimulation is thenconducted down the afferent branches of the nerves to the brain.Advantageously, windowed electrode assembly 200 locates pads 235 whencentered on the forehead such that virtually no electrical currentactually enters the brain. For example, a charge density of less than0.001 μC/cm² to no more than 0.1 μC/cm² of current penetrates to thecerebral cortex. Instead of inducing current in the brain, the wave ofpulses applied transcutaneously to the forehead induces neuronalsignaling events that alleviate neurological disorders such as epilepsy.Moreover, other conditions also respond to TNS therapy such asmigraines, acute brain injury, and chronic headache.

In an alternative embodiment, each window in windowed electrode assembly200 would be replaced by a inferiorly-to-superiorly oriented pair ofwindows such that the excitation from the corresponding pads/electrodesmay be performed in an afferent direction with regard to a given nervetrunk. Alternatively, each window may be replaced by amedially-to-laterally oriented pair of windows such that an ophthalmicnerve pair may be unilaterally stimulated. Regardless of the windowgeometry, gel pads 235 may be formed from a suitable conductive gel suchas a hydrogel and are received in corresponding windows in skin-facingfoam layer 220. In other words, gel pads 235 lies within correspondingwindows in skin-facing foam layer 220. The sidewalls for each windowthus comprise the edges of window in skin-facing foam layer 220. Priorto removal of release layer 240, gel pads 235 are sandwiched betweenrelease layer 240, the sidewalls for corresponding window, and a backwall for the corresponding window as formed by a conductive film patch230. An additional foam layer 210 also includes windows for gel pads235. Foam layers 210 and 220 are aligned such that their windows align.Each gel pad 235 is thus contained by the sidewalls of the correspondingwindows in foam layers 210 and 220 and a back wall formed by thecorresponding conductive film patch 230. A skin-facing surface of foamlayer 220 that faces release liner 240 is coated with a medical gradeadhesive such that foam layer 220 acts as a medical grade tape whenapplied to the skin of the forehead. Each window in additional foamlayer 210 receives a wire assembly 215 that is located anteriorly to thecorresponding conductive film patch 230. Each wire assembly 215comprises a conductive lead driving a metallic disk (electrical contact)so that, during use, a pulse generator coupled to the wire assemblies215 can drive electrical pulses through conductive film patches 230 andgel pads 235 to stimulate the desired nerve branches. A base foam layer205 provides a backing to the remaining electrode components to supporteach window back wall formed by the corresponding conductive patch 235and wire assembly 215.

An alternative embodiment for a windowed electrode assembly 300 isillustrated in FIGS. 3A, 3B, and 3C in which the flexible release lineris replaced by waxed paper flaps 330 and 325. FIG. 3A is a plan view ofa skin-facing surface of windowed electrode assembly 300 after removalof flaps 330 and 325 whereas FIG. 3B is a perspective view of windowedelectrode assembly prior to removal of the flaps. Flaps 3230 and 335function in the familiar “band aid” fashion such that each flap includesa projecting end that a user may readily pull on to release thecorresponding flap from windowed electrode assembly 300. Rather than usetwo foam layers having corresponding windows, each window in windowedelectrode assembly 300 is formed in a single foam layer 315. Thesidewalls for each window in foam layer 315 thus encase a correspondinggel pad 320. Gel pads 320 directly contact corresponding wire assemblies310 although a conductive patch similar to that described for windowedelectrode assembly 200 may also be used. Because the conductive patchesare absent in windowed electrode assembly 300, a foam backing layer 305not only supports the remaining components but also forms a back wallfor each window. A medical-grade adhesive on the skin-facing surface offoam layer 315 keeps flaps 325 and 330 adhered until they are removedand the skin-facing surface of foam layer 315 then applied to theforehead.

To aid in the alignment of windowed electrode assembly 300 on theforehead, a suitable anatomical landmark is the nasal midline. Windowedelectrode assembly 300 is aligned on the forehead so that its midlinealigns with the nasal midline. To assist such an alignment, a midlinealignment feature may be provided. For example, windowed electrodeassembly 300 may have an elongated hexagonal shape such that eachlongitudinal side forms a convex angle at the electrode midline. A usermay thus readily align features 301 with their nasal midline whenapplying electrode assembly 300 to their forehead.

The dimensions of a windowed electrode assembly such as assemblies 200and 300 depend upon the age of the patient. In a typical adult, theforamen (or notch) for the supratrochlear nerve is approximately 2.1 to2.6 cm from the nasal midline with regard to the corresponding orbit. Incontrast, the foramen (or notch) for the supraorbital nerve is locatedmore laterally from the nasal midline: e.g., approximately 3.2 cm fromthe nasal midline in adults. Given this anatomy, a convenientlongitudinal extent for a windowed electrode assembly such as assembly300 is 8.3 centimeters whereas its height at the midline is 3.5 cm. Themedial edge of each window for the corresponding gel pad 320 is 7 mmfrom the midline such that gel pads 320 are separated by 14 mm. Giventhe chevron shaping resulting from alignment features 301, each pad 320narrows by 12 degrees from a medial edge of a 27 mm to a lateral edge of20 mm over a width of 31.5 mm. The lateral edge of each pad 320 is thus38.5 mm from the nasal midline, Such a pad spacing assures that each pad320 is positioned to stimulate both the trunk of the supraorbital nerveand the trunk of the supraorbital nerve in an ophthalmic nerve pair forthe vast bulk of the adult population. But some adults will require evena greater pad width such as 34 mm to assure that the supraorbital nervesreceive adequate stimulation.

The bilateral stimulation from using at least two gel pads such as gelpads 235 or 320 is advantageous in that the function of brain structuresmay vary in the left and right hemispheres. Moreover, it is believedthat bilateral stimulation may lead to synergistic effects that increasetherapeutic efficacy. However, the present disclosure also includesembodiments in which the pads are positioned for unilateral nervestimulation as discussed earlier. For example, FIG. 4 illustrates awindow layout for a unilateral windowed electrode assembly 400. A firstpair of gel pads 112 a and 112 b are located for placement above thesupraorbital ridge at one side of the forehead. Similarly, a second pairof gel pads 114 a and 114 b are located for placement above thesupraorbital ridge on an opposing side of the forehead of a patient. Thefirst and second gel pad pairs are insulated from other by an insulativeconnection region 416. Each gel pad 112 a, 112 b, 114 a, and 114 b has awidth equal to or greater than the expected separation between asupraorbital nerve and the adjacent supratrochlear nerve in anophthalmic nerve pair. The electrode assembly 400 may be configured tostimulate both the right and left ophthalmic nerve pairs eithersimultaneously or asynchronously. The insulative connection region 416serves to assist a patient in lining up the electrode assembly 400 withthe midline of the nose to ensure proper placement of the electrodeassembly 400 over both ophthalmic nerve pairs. As discussed earlier, thesupratrochlear foramen (or notch) will typically be located about 2.1 to2.6 cm from the nasal midline of an adult patient. Similarly, thesupraorbital foramen (or notch) will typically be located about 3.2 cmfrom the nasal midline of an adult patient. The nerve fibers will tendto rise in a parallel fashion from notches. In other words, if anelectrode has a width sufficient to overlay the foramina for anophthalmic nerve pair, that same contact would also overlay thecorresponding ophthalmic nerve pair fibers if moved further up theforehead toward the hairline. Each electrode should thus have a widthand a positioning such that both nerves in the corresponding ophthalmicnerve pair are stimulated. By aligning region 416 with the nasalmidline, a patient may readily position windowed electrode assembly 400on the forehead without knowledge of the location of the ophthalmicnerve pairs or their foramina, thereby reducing the possibility ofinadequate stimulation due to errors in positioning of the electrodes.

In one embodiment, the mid-point of each of the gel pads isapproximately 2.5 cm (in other embodiments, such a mid-point may rangefrom 1.5 cm to 3.5 cm) from the nasal midline. The electrode size andthe inter-electrode distance may vary for children and adults, males andfemales based on anatomical differences. Each electrode is approximately32.5 mm in width by 12.5 mm in height and the distance between, forexample, the upper pair of electrodes 112 a and 114 a is 17.5 mm Theseparation between each electrode pair (e.g. between upper electrode 112a and the lower electrode 112 b is 20 mm. It is simpler, however, todirect the current neither in an afferent nor in an efferent fashion butinstead orthogonally across the fibers using just a single pair ofelectrodes as discussed with regard to electrode assemblies 200 and 300.

Referring again to FIG. 1, pulse generator 15 is portable and attachedto the belt of a patient 20. However, either a portable or non-portablepulse generator may be used. In alternative embodiments, a windowedelectrode assembly 100 may be integrated with a pulse generator.Regardless of whether a single pair of electrodes are used to stimulateboth ophthalmic nerve pairs or whether each ophthalmic nerve pair isstimulated by its own pair(s) of electrodes, the current from the pulsegenerator may be pulsed at a stimulus frequency between about 20 Hz andabout 300 Hz, at a pulse duration between 50 microseconds (μsec) and 250μsec, at an output current density of less than 25 mA/cm2 and an outputcharge density of less than 10 μ Coulomb/cm2 at the cerebral cortex forat least one-half to one hour per day. The pulsing may be performed in aduty cycle of 30 seconds of pulsing following by 30 seconds of rest.

In various embodiments, the stimulation is delivered at a specific pulsewidth or range of pulse widths (or pulse duration). The stimulation canbe set to deliver pulse widths in any range within a lower limit ofabout 10 microseconds and an upper limit of about 3 seconds. In variousembodiments, the stimulation can be set to deliver pulse widths in therange greater than and/or less than one or more of 50 ρsec, 60 μsec, 70μsec, 80 μsec, 90 μsec, 100 μsec, 125 μsec, 150 μsec, 175 μsec, 200μsec, 225 μsec, 250 μsec, up to 500 μsec. Those of skill in the art willrecognized that one or more of the above times can be used as a borderof a range of pulse widths.

It will be appreciated that the techniques and concepts discussed hereinare not limited to the specific disclosed embodiments. The appendedclaims encompass all such changes and modifications as fall within thetrue spirit and scope of this invention.

I claim:
 1. A windowed electrode assembly, comprising: a planar foamlayer having an adhesive surface, the planar foam layer defining atleast a first window on one side of a longitudinal center of thewindowed electrode assembly and a second window on an opposing side ofthe longitudinal center; a pair of gel pads, each gel pad being receivedby a corresponding one of the windows; a pair of conductive filmpatches, each conductive film patch being coextensive with and incontact with a side of a corresponding one of the gel pads; a pair ofelectrical contacts, each contact in contact with a corresponding one ofthe conductive film patches opposite the corresponding one of the gelpads; and a planar foam backing aligned with the planar foam layer toform a back wall for each window, wherein the mid-point of each of thegel pads is located between 1.5 cm and 3.5 cm from the longitudinalcenter.
 2. The windowed electrode assembly of claim 1, wherein theplanar foam layer comprises a single planar foam layer.
 3. The windowedelectrode assembly of claim 1, wherein the planar foam layer comprises aplurality of planar foam layers.
 4. The windowed electrode assembly ofclaim 1, wherein the planar foam layer and the planar foam backing eachhave a chevron shape forming an alignment feature at the longitudinalcenter of the windowed electrode assembly.
 5. The windowed electrodeassembly of claim 1, wherein each gel pad comprises a hydrogel.
 6. Thewindowed electrode assembly of claim 1, wherein each window has alateral extent greater than a spacing between a supraorbital nerve trunkand a supratrochlear nerve trunk in an ophthalmic nerve pair.
 7. Thewindowed electrode assembly of claim 6, wherein each window has alateral extent of approximately 30 mm.
 8. The windowed electrodeassembly of claim 1, wherein the planar foam layer and the planar foambacking each has a longitudinal extent of approximately 8 centimeters.9. The windowed electrode assembly of claim 1, wherein each electricalcontact comprises a metallic disk and an electrical lead coupled to themetallic disk.